Carburettor for motor vehicle

ABSTRACT

A mixture supply control system for an internal combustion engine of a motor vehicle, comprising an auxiliary fuel passage for providing communication between the fuel reservoir and the main mixture passage so as to supply additional fuel to the main mixture passage, valve means for opening and closing the auxiliary fuel passage in response to the temperature of the engine, an auxiliary air passage for providing communication between the valve means and a portion posterior to the throttle valve so as to supply additional air to the intake manifold, and temperature sensing means for controlling the opening and closing operations of the valve means in response to the temperature of the engine. The mixture supply control system supplies to the engine an appropriate amount of enriched mixture for the initial &#39;&#39;&#39;&#39;cold-engine&#39;&#39;&#39;&#39; and subsequent warming-up operations.

United States Patent Masaki et al. Dec. 19, 1972 1541 CARBURETTOR FOR MOTOR 1,544,350 6/1925 Sisson ..26l/39 D VEHICLE 2,074,471 3/1937 Holley et al. ..261/39 1) u 2,341,694 2/1944 Ceffey ...26l/D1G.,38 [72] inventors: Kenil Masakl, Yokosukal $11110 3,249,345 5/1966 Gast ..261/39 D Kat Tokyo, both of Japan 1,860,869 5/1932 Miquelon ..261/39 1) [73] Assig Nissan Motor p y Limited, 3,533,386 10/1970 Masakl etal. ..26l/D1G. l9

Yokohamajapan' Primary ExaminerTim R. Miles [22] Filed: Sept- 3, 19 Attorney-McCarthy, Depaoli, OBrien & Price [21] App]. No.: 69,396 ABSTRACT A mixture supply control system for an internal comt D t [30] Foreign Apphcatmn y a a bustion engine of a motor vehicle, compnsmg an aux- Sept. 9, 1969 Japan ..44/7l376 illary fuel passage for providing communication Sept. 9, 1969 Japan 4/ between the fuel reservoir and the main mixture 061. 3,1969 Japan ..44/790l2 pa age so as to upply additional fuel to the main mixture passage, valve means for opening and closing [5 1 11 C ..26 261/41 261/69 R, 1 the auxiliary fuel passage in response to the tempera- 26l/ I 261/121 A, 23/9 B4123/180 ture of the engine, an auxiliary air passage for provid- 123/180T ing communication between the valve means and a [5 Intportion posterior to the throttle valve so as to upply [58] Field Of Se8 D, 41 D, 69 121 additional air to the intake manifold, and temperature 261/1310 19; 123/1805 71 97 B sensing means for controlling the opening and closing I operations of the valve means in response to the teml References C'ted perature of the engine. The mixture supply control system supplies to the engine an appropriate amount UNITED STATES T of enriched mixture for the initial cold-engine and 3,059,909 11/1962 Wise ..261/39 D subsequent warming-up operations, 2,675,792 4/1954 Brown et al. ..261/39 D I I 2,771,282 11/1956 Olson et al ..26l/4l D 2 Claims, 4 Drawing Flgures 460 4 46k 4616f l \\\\z\\\\\\\\\ AIR -I- 7 Q I 46 46' 3210 I6 "Ill", I j 461 I "1 C '4' E l 6 E.

l I i .1

w V I a 0 a. 2 l' A Z P'ATENTED DEC 19 I972 3 705 444 INVENTORS KENJI MASAK! BY SiNZO KAI'O ATTORNEYS PATENTED DEC 19 I972 SHEET 3 OF 4 INVENTORS KENJI MASAKI BY smzo KATO ATTORNEYS PATENTEU nEc 19 m2 SHEET t 0F 4 CARBURETTOR FOR MOTOR VEHICLE This invention relates to carburettors for internal combustion engines used in motor vehicles and particularly to carburettors having a mixture supply control system for feeding to the engine a satisfactory amount of enriched air-fuel mixture for the initial cold-engine and subsequent warm-up operations.

Nowadays, air pollution is a serious social problem. Although there are a number of sources of noxious air pollutants, the pollutants emitted in engine exhaust gases are increasingly prominent. With a view to minimizing such emissions, various vehicular air-pollution preventive methods have been proposed including the improvements of the engine and/or carburettor performance.

As is well known in the art, the engine exhaust emission of the noxious air pollutants such as carbon monoxide, hydrocarbons and nitrogen oxides can be reduced to a minimum only if an air-fuel mixture is burned completely at its stoichiometric ratio in the combustion chamber. It is found, however, quite difficult to accomplish compete combustion in the engine for all the varying driving conditions of the vehicle. As a matter of fact, the above noxious pollutants are produced in different quantities varying in the kind of the pollutants dependent on the running conditions of the engine. For instance, the quantity of nitrogen oxides emitted is large when the air-fuel mixture is lean while the quantities of carbon monoxide and hydrocarbons are large when the mixture is rich. The emission of nitrogen oxides can be made so small, however, as to cause no serious air-pollution problem even with a lean mixture, if the engine has not fully warmed up. Under these circumstances, there has been a growing tendency to construct the carburettors of known types in a manner to provide a lean mixture without or with little respect to the varying driving conditions of the vehicle.

This tendency to provide a lean mixture inevitably invites deterioration of drivability of the vehicle due to the degradation of operational performance'of the engine. The drivability deterioration is often experienced as such phenomena as engine stalling when starting, lack of power for acceleration or knocking of the engine under all driving conditions from low to intermediate speed ranges of the vehicle, and occurs particularly when the ambient temperature is low and/or when the engine is being warmed up. In addition, socalled cold driving is often performed these days bymost drivers without allowing ample time for warmingup, thus affecting the drivability of the vehicle still more.

In general, gasoline as usually used for fuel of the motor vehicle does not satisfy all of the engine operat ing requirements during the cold driving because of its lack of volatility. In order to acquire a stable drivability of the vehicle, an appropriate amount of enriched airfuel mixture is needed especially for cold driving. As has been discussed, however, existing carburettors are set to provide lean mixture so as to reduce the emission of the noxious air pollutants, thus inviting deterioration in drivability. This deterioration is encountered in existing carburettors, since when carburetor operation is changed from the slow-running mixture circuit to the main mixture circuit little or no mixture is supplied to the intake manifold for the transitional operation.

In order to overcome these drawbacks, there has been proposed a method in which the mixture flow rate supplied through the two circuits is increased for this particular driving conditions. This method aids in improvement of the drivability but a large amount of the air pollutants are emitted into the open air from the exhaust pipe. Nowadays, however, this method can not be employed under the regulations of the law.

This invention is based on the experiments conducted by us using carburettors set to to provide a lean air-fuel mixture, which experiments have revealed that during the cold driving" an improvement of drivability is effected if an enriched mixture is supplied through the main mixture circuit rather than through the slowrunning mixture circuit. This means that an enriched air-fuel mixture is fed to the engine for the initial coldengine and subsequent warm-up operations. These preparations necessary for warming up the engine up to a predetermined level before starting to move the vehicle are known to continue for 5 to ISminutes depending upon the ambient temperature. The temperature level thus determined previously is, for example, C in terms of the temperature of the engine cooling liquid. Considering the short period ranging from 5 to 15 minutes, the emission of the pollutants contained in the exhaust gases during the cold driving is not considerable when compared with the total amount exhausted during all driving conditions, even if an overrich mixture is consumed in the engine during this period.

The mixture supply control system proposed in this invention is constructed and arranged in such a 'manner that an air-fuel mixture having a sufficiently rich airfuel ratio is fed to the engine during the initial cold-engine and subsequent warm-up operations by opening an auxiliary fuel passage. This auxiliary fuel passage is provided in the system so as to communicate both with the main mixture circuit and with the float chamber.

Thus, it is an object of the invention to provide a carburettor of a type adapted to feed to the engine an enriched mixture during the initial cold driving of the vehicle and to feed a usual lean mixture as soon as the engine has been sufficiently warmed up.

Another object is to provide a carburettor having an auxiliary fuel passage for providing communication between the main mixture passage and the float chamber and valve means for opening and closing the auxiliary fuel passage responsive to the temperature of the engine, thereby improving the drivability of the vehicle.

In the drawings:

FIG. 1 is a schematic sectional view of an overall construction of the carburettor having a mixture supply control system according to the invention, in which the opening and closing of the auxiliary fuel passage is controlled by a piston valve assembly responsive to the intake manifold vacuum and the temperature condition of the engine;

FIG. 2 is similar to FIG. 1 but shows a modification of the system, in which an additional port is provided to feed to the engine a sufficient amount of mixture during the warming-up period;

FIG. 3 is also similar to FIG. 1 but shows another modification of the system, in which the fuel flow rate passing through the auxiliary fuel passage is controlled by a solenoid valve assembly and in which the auxiliary passage opens to the slow-running port of the carburettor; and

FIG. 4 is similar to FIG. 3 but shows a modification of the system, in which the fuel flow rate is controlled by a diaphragm valve assembly.

Throughout the accompanying drawings, like characters and reference numerals will designate corresponding parts or elements. The mixture supply control systems implementing the invention, which are generally denoted by numerals 10, 10', 10" and 10, respectively, in FIGS. 1, 2, 3 and 4, are used in a conventional carburettor 12. The carburettor 12 is, as is well known, provided with a throttle valve 14, a venturi 16, a small venturi 16, a main mixture circuit 18, an idling and slow-running mixture circuit 20 and a float chamber 22. The throttle valve 14 is mounted on a rotatable shaft 14a .in the carburetion induction passage and is herein shown as substantially fully closed to effect idling or deceleration of the motor vehicle. The main mixture circuit 18, through which an air-fuel mixture is supplied to the carburetor induction passage for'relatively heavy load operation such as acceleration, cruising or high speed operation of the engine opens into the small venturi 16'. The idling and slow running mixture circuit 20 for idle or light load operation is opens to the induction passage of the carburetor downstream of the venturi 16 through a slow-running port 24 and an idling port 26. The slow-running port 24 is located at a position closely adjacent to the periphery of the throttle valve 14 when it is substantially closed, while the idling port 26 is located posterior to or downstream of the throttle valve 14. Designated by numeral 28 is an idling adjustment screw for adjusting the flow rate of the mixture through the idling port 26.

There is provided in the main mixture circuit 18 a main jet 30, a main fuel and air mixer 32 and a main nozzle 34 in this sequence from the float chamber 22. The main fuel and air mixer 32 has formed at its bottom an orifice 32a and at its top an air bleed 32b vented from the open air. The orifice 32a and air bleed 32b are so calibrated as to providea desired amount of lean airfuel mixture, so that a lean mixture is delivered through the nozzle 34 to the carburetor induction passage, so as to reduce the air pollutant content in the engine ex haust gases. In operation, with the throttle valve 14 substantially fully opened for a relatively heavy load operation, a sufficient vacuum is established in the small venturi 16' due to the fact that a considerable amount of air is passing through the small venturi 16 for this particular operation. Then, a desired amount of fuel which is metered by the main jet 30 is atomized by the main fuel and air mixer 32 to provide an air-fuel mixture, which is drawn through the main nozzle 34 into the small venturi 16' by the vacuum established therein.

In addition to the slow-running port 24 and idling port 26 there is provided in the idling and slow-running mixture circuit 20 a slow-running fuel and air mixer 36 which has formed at its bottom an orifice 36a and a first from the ambient air at desired flow rates. While the engine is being driven under idling or light load conditions with the throttle valve 14 substantially fully closed, the air flow rate delivered into the engine is not large and, therefore, little or no vacuum is established thesmallventuri 16'. Thus, a meteredair-fuel mixture is supplied to the engine through the slow-running port 24 and/or idling port 26.

According to this invention, there is provided in the conventional carburettor mentioned above a mixture supply control system l0, l, or 10" which comprises an auxiliary fuel passage 38 leading from the float chamber 22 and opening into the main mixture circuit 18, a valve assembly 40 for opening and closing the auxiliary fuel passage 38 in response to the temperature condition of the engine, an auxiliary air passage 42 leading from the valve assembly 40 and opening into the carburetor induction passage; and

temperature sensing means 44 for controlling the opening and closing of the valve assembly 40 in response to the temperature of the engine.

The auxiliary fuel passage 38 is shown to open to the main mixture circuit 18 downstream of the main jet 30 and upstream of the two fuel and air mixers 32 and 36, but may open upstream of the main jet 30. The valve assembly 40 implementing this invention may be of any type such as a piston, a solenoid or a diaphragm type, if it can be actuated to control the opening and closing of the auxiliary fuel passage 38 in responseto the temperature condition of the engine. The mixture supply control systems 10, 10', 10" andl0 of the invention employing the different type valve assemblies listed above will be described with reference to the accompanying drawings. The auxiliary air passage 42 may either open to the carburetor induction passage or may lead to the slow port 25. The air passage 42 leading to the induction passage operates to actuate the valve assembly- 40 when a high vacuum is produced in the intake manifold. To the contrary, the air passage 42 communicates with the slow-running port 24 and operates partially to actuate the valve assembly 40 and partially to feed additional air to the engine through the slowrunning port 24. The temperature sensing means 44 functions to detect the temperature at which the engine is being driven. This temperature detectionmay be carried out in this invention by means of a bimetal device 44, which may be located in the neighborhood of the carburettor 12 or immersed in the engine cooling liquid. The means 44 is adapted to control mechanically or electrically the operation of the valve assembly 40 when the temperature is below a predetermined level, namely, when the engine is running cold.

An example of a mixture supply control system to which this invention is directed is illustrated in FIG. 1. In this embodiment, the mixture supply control system designated by numeral 10 has a valve assembly 40 of piston type, an auxiliary air passage 42 leading to the induction passage downstream of the idling port 26 and a bimetal device 44 acting as temperature sensing means. The piston valve assembly 40 is formed of two portions 46 and 48, one portion being mounted fixedly on the outside wall of the carburettor and the other portion being mounted inside the carburetor and below the level of the liquid fuel contained in the float chamber 22. The portion 46 comprises a housing 46a ioeou 0054 defining a suction chamber 46b which communicates both with the float chamber 22 through a bore 460 and with the auxiliary air passage 42 through a suction conduit 46d and an orifice 46a. In the suction chamber 46b is accommodated a suction operated piston 46f 5 adapted to be axially movable with a piston rod 46g. This piston rod 46g extends through the bore 46c into the float chamber 22 and is biased by a compression spring 46h which is seated on two spring seats 46i and 46j, one being located at one end of and forming one and wall of the suction chamber 46b and the other being located at one end of the piston rod 46g. On an extension 46k of the housing 46a is mounted fixedly a bimetal member 44a of the bimetal device 44 which carries a conical member 44b. This conical member 44b is so formed as to be air-tightly seated, when the bimetal member 44a bends in an air vent 461 having an inwardly inclined inlet surface and which leads to the suction conduit 46d and the suction chamber 46b, as shown.

The other portion 48 of the piston valve assembly 40 comprises a housing 48a which is fixedly threaded into a portion of the carburetor body defining the float chamber 22. By the housing 48a is defined a fuel chamber 48b leading to the auxiliary fuel passage 38 and communicating with the float chamber 22 past a valve member 48c accommodated in the housing 48a. This valve member 480 has a conical tip 48d and radially extending tapered portion 48e and is always biased by a compression spring 48f. The valve member 48c is axially movable to shut off the fuel flow passing through a bore 483 formed coaxially therewith.

The bimetal member 44a is adapted to retain the member 44b spaced from the vent 461 while the temperature surrounding the carburettor 12 is still low, namely, not exceeding a predetermined level indicating the completeness of the engine warming-up. When the temperature exceedsthe predetermined value, however, the bimetal member 44a begins to bend downwardly in the drawing to shut off the air flow through the air vent 461 into the'suction chamber 46b. The spring seat 46g and the valve member 480 are always in abutting engagement with each other due to the two springs 46h and 48f forcing them in opposing directions. The compression force of the spring 46h is selected to be stronger than that of the spring 48f so that the piston rod 46g is normally forced downwardly of the drawing together with the valve member 48c inasmuch as n other force is imposed on the suction piston 46f. Thus, the axial position of the suction piston 46f can control the effective cross-sectional area defined between the bore 48g and the conical tip 48d of the valve member 480. For example, when the suction piston 46f is forced to be in contact with the spring seat 46i by the compression force difference between the ring 46h and the spring 48f, the effective cross-sectional area between the bore 48g and the conical tip 48d is large enough to admit a desired amount of fuel flow therethrough. When the suction piston 46f is moved upwardly a distance exceeding the stroke of the valve member 480, however, the tapered portion 48e of the valve member 48c cuts off the fuel flow by the action of the spring 483 independently of any further movement of the suction piston 46f. In this instance, the effective area of the orifice 46s in the suction conduit 46d is so sized as to choke the air flow passing therethrough even when the pressure difference between the suction chamber 46b and the carburetor induction passage is large. I

With this construction arrangement of the mixture supply control system 10, the air vent 46! is shown to be open to the ambient air, since the bimetal member 44a holds the member 44b spaced from the vent 46b while the temperature remains below a predetermined level. For this cold driving or warming-up of the engine, there is no pressure difference between the suction chamber 46b and the float chamber 22. Under this condition, the valve member 48c is forced downwardly by the action of the spring 46h overcoming the action of the spring 48f. The effective cross-sectional area thus formed between the inside surface of the bore 48g and the outside surface of the conical tip 48d can pass a sufficient flow of fuel in addition to the usual fuel flow which is fed through the main jet 30. As has been discussed in detail, a satisfactory amount of enriched mixture is thus fed, in this instance, to the engine through the slowrunning port 24 and/or idling port 26 before the engine has been fully warmed up.

When the engine has reached its normal operating temperature and the temperature therefore exceeds the predetermined level, the bimetal member 44a begins to warp downwardly thereby to close the air vent 461. Then, there is no communication between the suction chamber 46b and the ambient air. This admits the vacuum'in the carburetor induction passage through the auxiliary air passage 42, orifice 461 and suction conduit 46d into the suction chamber 46b. The vacuum thus established in the suction chamber 46b operates so that the piston 46f is moved upwardly against the action of the spring 46h together with the piston rod 46g. As a result, the valve member 48c is forced upwardly by the spring 48f to shut off the fuel flow to be introduced through the additional fuel passage 38. With this fuel passage completely closed, a suitable amount of lean mixture is delivered to the engine, after the engine has reached its normal operating temperature. This means that, for relatively heavy load operations of the engine, only an appropriate amount of fuel is fed to the atomizer 32 through the main jet 30.

The valve assembly as herein used may be constructed and arranged in many other ways, an example being shown in FIG. 2. Referring now to FIG. 2, there is provided a piston operated valve assembly 40' whose operation is substantially similar to that of the valve assembly 40 described with respect to FIG. I but whose construction is slightly different therefrom. The difference is in that an additional port 50 is provided in the carburetor induction passage at a position between the idling port 26 and the port at which the additional air passage 42 opens into the carburetor induction passage. The additional port 50 is arranged to communicate with the slow-running fuel and air mixer 36 and is controlled by another valve assembly. In this embodiment, the additional valve assembly 52 is, by way of example, of solenoid type but may be of any other conventional type as far as its operation is controlled in response to the temperature of the engine and/or to a the driving condition of the engine such as the intake manifold vacuum.

The construction arrangement of the piston valve assembly 40' is, furthermore, a little different from that of the piston valve assembly 40 in that the bimetal member 44d of the bimetal device 44 is accommodated in a suction chamber 40'a communicating with the auxiliary air passage 42 and in that an orifice 40b isprovided in the housing 46a and opens directly into the ambient air. In view of this, while the bimetal member 440 holds the, member 44b spaced from the vent 461 during the cold running of the engine, the conical member 44b of the bimetal member 44a is air-tightly seated in the inwardly inclined surface of the. air vent 461. Since the orifice 40'b is opens to the ambient air, the suction chamber 46b is kept at an atmospheric pressure 'unless the intake manifold vacuum is introduced thereinto through the air vent 461. When the bimetal member 44a bends upwardly of the drawing at a temperature above the predetermined value, air from the suction chamber 46b is drawn into the carburetor induction passage through the air vent 461 and the auxiliary air passage 42. The orifice 40'b is so sized inits effective area as to allow therethrough introduction of a limited amount of air, thus maintaining the suction chamber 46b at a reduced pressure nearly equal to the intake manifold vacuum. With the suction chamber 46b held under vacuum, in this way, the suction piston 46f is moved upwardly to close communication between the float chamber 22 and the auxiliary fuel passage 38.

It should be noted here that the mixture supply control system 10 is provided with an additional port 50.

whose effective area is regulated by a solenoid valve assembly 52. The solenoid valve assembly 52 has a needle element 52a, which is actuated by a solenoid device 54 consisting of a solenoid coil 54a and an axially movable element 54b. The needle element 52a, which is coaxially integral with the movable element 54b, is normally kept seated on the inside of the additional port 50 so as to block communication between the carburetor induction passage and. an additional mixture passage 56. The movable element 54b is adapted to e retracted and protruded by the solenoid coil 54a together with the needle element 52a. This additional mixture passage 56 is adapted to deliver an air-fuel mixture from the slowrunning fuel and air mixer 36 to the additional port 50. The solenoid coil 54a is electrically connected in series to a power source 58 through a main switch 60 and thermoswitch 62 by a line'64. If desired, a vacuum switch 66 may be added in the line 64 in parallel with the thermoswitch 62 to constitute an OR circuit, as shown. The thermoswitch 62 is constituted, for instance, as a normally-open relay switch which is connected to and actuated by a temperature detector (not shown). This temperature detector is adapted to detect the temperature of the engine, so that it may be provided directly on the wall or in the air cleaner (not shown) of the carburetor 12 or may be immersed in the engine cooling liquid, as'the case may be. The operaclose the vacuum switch 66 when the vacuum exceeds a predetermined level. In short, the thermoswitch 62' is closed during the cold driving operation of the engine whilst the vacuum switch 66 is closed during the high vacuum condition such as during deceleration.

Thus, the solenoid coil 54a canbe energized not only when the engine is being driven cold but when the vehicle is deceleratingQif the vacuum switch 66 is interposed in the line 64. With the solenoid coil 54a energized the movable element 54b is moved to a position in which the needle element 52a is unseated from the inside of the additional port 50, providing communication between the idling and slow-running mixture circuit 20 and the carburetor induction passage. in this manner, the mixture supply control systeml0' of FIG. 2 can feed to the engine a sufficient amount of enriched mixture for cold running. Moreover, since the additional port 50 is also opened during deceleration even after the engine has been warmed up, the system 10 can also feed to the engine a sufficient amount of mixture without detriment to the combustion performance for its particular condition. Suchreduction of air pollu- I tant emission during deceleration can be said to result from the fact that under the high vacuum in the intake manifold a considerable amount of air is drawn from the second air bleed 36c into the intake manifold in addition to a certain amount of air-fuel mixture. Meanwhile, the flow rate of the additional air may be regulated to offer an overall air-fuel mixture in an amount and mixture ratio suitable for complete com bustion in the engine.

In FIG. 3, there is shown another modification 10" of the mixture supply control system of the invention, in which the fuel flow rate passing through the additional fuel passage 38 is controlled by a solenoid valve assembly 68. Moreover, it should be appreciated that the additional air passage 42 opens to the slow-running port 24 so as to supply an additional air to the engine therethrough.

The solenoid valve'assembly 68 has two needle elements 68a and 68b which are axially movable when actuated by a solenoid device 70 consisting of ,a solenoid coil 70a and movable core 70b made coaxially integral with the two needle elements 68a and 68b. The needle element 68a is constructed to be received air-tightly and axially movably on the inside wall of the solenoid valve assembly 68. During the cold driving of the engine, the needle element 68a is held seated on the outlet of an air vent 700 provided on a housing 70d, while the other needle element 68b is unseated from a bore 72 formed in a member screwed into a sort in a body of the carburetor defining the float chamber 22. In the housing 70d are provided an atmospheric chamber 70c communicating with the carburetor inductionpassage through the auxiliary air passage 42 and a compression spring 70f biasing the solenoid core 70b downwardly in the drawing. The bore 72, whose upper end acts as a valve seat, for the needle element 68b communicates with the main mixture circuit 18 through the auxiliary fuel passage 38. After the engine has been warmed up sufficiently with the solenoid coil 70a being de-energized, the solenoid core 70b is urged downwardly by power source 58 through the main switch 60 and the thermoswitch 62 in this sequence.

In operation, when theengine is being driven cold with the thermoswitch 62 closed, the solenoid coil 70a is energized to pull the solenoid core 70b upwardly against the action of the spring 70f together with the two needle elements 68a and 68b. This causes the needle element 68a to be seated in the outlet of the air vent 70c and the needle element 68b to be unseated from the bore' 72 to provide communication between the float chamber 22 and the auxiliary fuel passage 38. Therefore, a suitable amount of enriched mixture is supplied to the engine for the cold running condition. When the temperature of the engine is above the predetermined value with the thermoswitch 62 being open, the solenoid coil 70a is being de-energized so that the two needle elements 68a and 68b are forced downwardly, respectively, to allow air to flow into the chamber 70:: and to block the fuel flows passing through the bore 72. The air flow to the slow'running port 24 through theadditional air passage 42 when a vacuum is present at the slow-running port 24. This additional air flow aids in providing a leaner mixture in an effective fashion to the engine to thereby reduce the hydrocarbon and/or carbon monoxide content in the engine exhaust gases when the engine has reached its normal operating temperature, especially during deceleration.

Referring to FIG. 4, the additional fuel flow is controlled by a diaphragm valve assembly 74 in cooperation with a bimetal device 76 in the mixture supply control system 10". The diaphragm valve assembly 74 and the bimetal device 76 are operated in response to the intake manifold vacuum and to the engine temperature, respectively. The diaphragm valve assembly 74 has an atmospheric chamber 74a vented to the atmosphere through a bore 74b communicating with the float chamber 22 and a suction chamber 74c communicating with the slow-running port 24 by way of a chamber 76a in the bimetal device 76 and the additional air passage 42. The suction chamber 74c is hermetically sealed off from the atmospheric chamber 74a by a diaphragm member 74d to which is rigidly connected a needle element 74e extending into the float chamber 22 through the bore 74b. A compression spring 74f acts on the suction side of the diaphragm member 74d, so that the diaphragm member 74d and accordingly the needle element 74e are always urged downwardly in FIG. 1. The bimetal device 76 has a suction chamber 76a providing communication between the auxiliary air passage 42 and the suction chamber 74c of the diaphragm valve assembly 74. The suction chamber 76a is defined by a housing 76b which has an air vent 76c to the atmosphere and a bimetal member 76d mounted rigidly on the wall thereof. At the free end of the bimetal member 76d a conical member 76c is carried. While the bimetal member 76d remains substantially straight, the tip member 76e is adapted to be in abutting engagement with the air vent 760 to prevent air flow therethrough. The compression force of the spring 74f is selected in such a manner as to be overcome due to the intake manifold vacuum to be introduced.

With the air vent 76c sealed during the cold running of the engine, the intake manifold vacuum acts in the suction chamber 740 of the diaphragm valve assembly 74. Due to the pressure difference between the two chambers 74a and 740, the diaphragm member 74d is moved upwardly together with the needle element 74e against the action of the spring 74f, as shown, thus providing communication between the float chamber 22 and the auxiliary fuel passage 38. As a result, a suitable amount of enriched mixture can be supplied to the engine for the colddriving, as has been discussed. After the engine has reached its normal operating temperature, the bimetal member 76d bends upwardly to open the air vent 760. Then, the suction chamber 740 becomes atmospheric so-that the diaphragm member 74d is forced downwardly by the spring action together with the needle element 74e. This closes the bore 72 and therefore shuts off the additional fuel flow delivered through the auxiliary fuel passage 38, thus an appropriate amount of lean mixture is supplied to the carburetor induction passage through the mixture circuit 18 for the normal driving condition. Moreover, additional air is delivered to the slow-running port 24 to thereby increase the air-fuel ratio to a suitable lean side.

It will now be appreciated from the foregoing description that, according to one important aspect of the invention, an enriched mixture is supplied to the engine during cold running of the engine, whereby-the engine can be driven with satisfactory performance quality as well as with a short warming-up period. According to another important aspect of the invention, a lean mixture is supplied to the engine with the engine fully warmed up. With this in mind, a carburetor having the mixture supply control systemof the invention can reduce significantly the overall air pollutant emission contained in the engine exhaust gases without detriment to the drivability of the vehicle.

What is claimed is:

1. In a carburetor for an internal combustion engine of a motor vehicle having a main mixture circuit adapted to supply an air-fuel mixture to the carburetor induction passage for high-speed and acceleration operations of the engine, an idling and slow-running mixture circuit adapted to supply a mixture to the carburetor induction passage for slow-running and deceleration operations of the engine, a throttle valve disposed in the carburetor induction passage for controlling the quantity and air-fuel ratio of the mixture supplied by the carburetor to the engine, and a fuel supply reservoir which supplies fuel to the two circuits; a mixture supply control system comprising in combination an auxiliary fuel passage providing communication between said fuel reservoir and said main mixture circuit so as to supply additional fuel to said main mixture circuit, a suction-operated piston valve assembly for opening and closing said auxiliary fuel passage in response to the temperature of the engine, an auxiliary air passage providing communication between said suction-operated piston valve assembly and the carburetor induction passage downstream of said throttle valve for supplying additional air to the carburetor induction passage, and a bimetal device for controlling the opening and closing operations of said suction-operated piston valve assembly in response to the temperature of the engine for thereby supplying to the engine an appropriate amount of enriched mixture for the initial cold-engine" and subsequent warmingup operations, said suction-operated piston valve assembly including two portions, one portion consisting of a housing mounted on the outside surface of the carburetor and defining a suction chamber, which housing has therein an axially movable piston and an air vent which is vented from the ambientair, said suction chamber communicating with said airpassage through an orifice and with the fuel reservoir through a bore whichhas therein an axially movable piston rod connected to said first-mentioned axially movable piston and extending into said fuel reservoir and a compression spring biasing said piston rod toward said fuel reservoir, and the other portion consisting of a housing mounted in the body of the carburetor below the level in the liquid fuel contained in said fuel reservoir and defining a fuel chamber, which housing has therein an axially movable needle element in abutting engagement with said piston rod at their ends and a compression spring selected to be weaker in force than the firstmentioned compression spring and biasing said needle element in a direction opposite to that of the first-mentioned compression spring, said fuel chamber communicating with said fuel passage and with said fuel reservoir through a bore in the second-mentioned housing, said needle element having a radially extending tapered portion for shutting off the fuel flow through said second-mentioned bore, whereby with no vacuum present in said suction chamber said piston rod forces said needle element in a direction to open the secondmentioned bore, while with a vacuum present in said suction chamber said piston rod is urged due to he vacuum in a direction :to close the second-mentioned bore, and said said bimetal device including a bimetal member mounted outside the first-mentioned housing of said piston valve assembly and carrying a conical member to be seated air-tightly on said air vent, said bimetal member being adapted to hold said conical member so asto open said air vent when the engine is cold and being adapted to bend toward said air vent so as to close said air vent as soon as the temperature of the engine exceeds a predetermined value. I

2. In a carburetor for an internal combustion engine of a motor vehicle having a fuel supply reservoir, a carburetor induction passage, a throttle valve disposed in said carburetor induction passage, a main venturi and a small venturi, the combination comprising a inain mixture circuit opening into said small venturi for supplying an air-fuel mixture to said carburetor induction passage for high-speed and acceleration operations of the engine, said main mixture circuit having a main fuel jet communicating with said fuel supply reservoir, a main fuel and air mixer communicating with said main fuel jet and a main nozzle opening into said small venturi, said main fueland air mixer having formed at its bottom an orifice and its' top an air bleed vented from the atmosphere, the effective cross-sectional areas of said orifice and said air bleed being so calibrated as to provide a desired amount of lean air-fuel mixture so that a lean mixture is produced in said main mixture circuit for delivering to the engine, an idling and slowrunning mixture circuit opening into said carburetor induction passage downstream of said main venturi for supplying an air-fuel mixture to said carburetor induction passage for low-speed and deceleration operations of the engine, said idling and slow-running mixture circuit having a slow-running port located at a position closely adjacent to the periphery of said throttle valve when it is substantially fully closed and an idling port located downstream of said throttle valve, said idling and slow-running mixture circuit having a slow-running fuel and air mixer which has formed at its bottom an orifice and a firstair bleed vented from the ambientatmosphere and a second'air bleed downstream of said first air bleed, the effective cross-sectional areas of said first and second air bleeds being so calibrated as to admit air from the ambient atmosphere at desired flow rates to providethe air-fuel mixture for the low-speed and deceleration operations of the engine, an auxiliary fuel passage providing communication between said fuel supply reservoir and said main mixture circuit so as to supply additional fuel to said main mixture circuit, a suction-operated piston valve assembly for opening and closing said auxiliary fuel passage in response to the temperature of the engine, an auxiliary air passage providing communication between said suctionoperated piston valve assembly and said carburetor in? duction passage downstream of said throttle valve for supplying additional air to said carburetor induction passage, and a bimetallic device for controlling the opening and closing operations of said suctionoperated piston valve assembly in response to the temperature of the engine for thereby supplying to' the engine an appropriate amount of enriched air-fuel mixture for the initial cold-engine and subsequentwarm ing-up operations, said suction-operated piston valve assembly including first and second portions, said first portion consisting of a housing mounted on the outside surface of the carburetor and having a suction chamber and an air vent from the ambient atmosphere, an axially movable suction-operated piston accommodated in said suction chamber, said suction chamber'communicating with said auxiliary air passage through an orifice and 'with said fuel supply reservoir through a bore,

an axially movable piston rod accommodated insaid bore and connected to said suction-operated piston, said axially movable piston rod extending into said fuel supply reservoir, and a compression spring biasing said piston rod toward said fuel supply reservoir, and said second portion consisting of a housing mounted in the body of the carburetor below the level in the liquid fuel in said fuel supply reservoir, a fuel chamber defined in said second-mentioned housing and leading to said auxiliary fuel passage througha bore and communicating with said fuel supply reservoir, an axially movable needle element accommodated in said second-mentioned housing and in abutting engagement with said axially movable piston rod at their ends and a compression spring selected to be weaker in force than the firstmentioned compression spring and biasing said needle element in a direction opposite to that of the first-mentioned-compression spring, said needle element having a radially extending tapered portion for shutting off the fuel flow through said second-mentioned bore, whereby with no vacuum present in said suction chamber said piston rod forces said needle element in a direction to open said second-mentioned bore, while with a vacuum present in said suction chamber said piston rod is urged due to the vacuum in a direction to close the second-mentioned bore, and said bimetal device including a bimetal member mounted outside the firstimentioned housing of said suction-operated piston valve assembly and carrying a conical member to be seated air-tightly on said air vent, said bimetal member being adapted to hold said conical member so 

1. In a carburetor for an internal combustion engine of a motor vehicle having a main mixture circuit adapted to supply an airfuel mixture to the carburetor induction passage for high-speed and acceleration operations of the engine, an idling and slowrunning mixture circuit adapted to supply a mixture to the carburetor induction passage for slow-running and deceleration operations of the engine, a throttle valve disposed in the carburetor induction passage for controlling the quantity and air-fuel ratio of the mixture supplied by the carburetor to the engine, and a fuel supply reservoir which supplies Fuel to the two circuits; a mixture supply control system comprising in combination an auxiliary fuel passage providing communication between said fuel reservoir and said main mixture circuit so as to supply additional fuel to said main mixture circuit, a suction-operated piston valve assembly for opening and closing said auxiliary fuel passage in response to the temperature of the engine, an auxiliary air passage providing communication between said suction-operated piston valve assembly and the carburetor induction passage downstream of said throttle valve for supplying additional air to the carburetor induction passage, and a bimetal device for controlling the opening and closing operations of said suction-operated piston valve assembly in response to the temperature of the engine for thereby supplying to the engine an appropriate amount of enriched mixture for the initial ''''coldengine'''' and subsequent warming-up operations, said suctionoperated piston valve assembly including two portions, one portion consisting of a housing mounted on the outside surface of the carburetor and defining a suction chamber, which housing has therein an axially movable piston and an air vent which is vented from the ambient air, said suction chamber communicating with said air passage through an orifice and with the fuel reservoir through a bore which has therein an axially movable piston rod connected to said first-mentioned axially movable piston and extending into said fuel reservoir and a compression spring biasing said piston rod toward said fuel reservoir, and the other portion consisting of a housing mounted in the body of the carburetor below the level in the liquid fuel contained in said fuel reservoir and defining a fuel chamber, which housing has therein an axially movable needle element in abutting engagement with said piston rod at their ends and a compression spring selected to be weaker in force than the first-mentioned compression spring and biasing said needle element in a direction opposite to that of the first-mentioned compression spring, said fuel chamber communicating with said fuel passage and with said fuel reservoir through a bore in the second-mentioned housing, said needle element having a radially extending tapered portion for shutting off the fuel flow through said second-mentioned bore, whereby with no vacuum present in said suction chamber said piston rod forces said needle element in a direction to open the second-mentioned bore, while with a vacuum present in said suction chamber said piston rod is urged due to he vacuum in a direction to close the second-mentioned bore, and said said bimetal device including a bimetal member mounted outside the first-mentioned housing of said piston valve assembly and carrying a conical member to be seated air-tightly on said air vent, said bimetal member being adapted to hold said conical member so as to open said air vent when the engine is cold and being adapted to bend toward said air vent so as to close said air vent as soon as the temperature of the engine exceeds a predetermined value.
 2. In a carburetor for an internal combustion engine of a motor vehicle having a fuel supply reservoir, a carburetor induction passage, a throttle valve disposed in said carburetor induction passage, a main venturi and a small venturi, the combination comprising a main mixture circuit opening into said small venturi for supplying an air-fuel mixture to said carburetor induction passage for high-speed and acceleration operations of the engine, said main mixture circuit having a main fuel jet communicating with said fuel supply reservoir, a main fuel and air mixer communicating with said main fuel jet and a main nozzle opening into said small venturi, said main fuel and air mixer having formed at its bottom an orifice and its top an air bleed vented from the atmosphere, the effective cross-sectional areas of said orifice and said air bleed being so calibrated as to provide a desired amount of lean air-fuel mixture so that a leaN mixture is produced in said main mixture circuit for delivering to the engine, an idling and slow-running mixture circuit opening into said carburetor induction passage downstream of said main venturi for supplying an air-fuel mixture to said carburetor induction passage for low-speed and deceleration operations of the engine, said idling and slow-running mixture circuit having a slow-running port located at a position closely adjacent to the periphery of said throttle valve when it is substantially fully closed and an idling port located downstream of said throttle valve, said idling and slow-running mixture circuit having a slow-running fuel and air mixer which has formed at its bottom an orifice and a first air bleed vented from the ambient atmosphere and a second air bleed downstream of said first air bleed, the effective cross-sectional areas of said first and second air bleeds being so calibrated as to admit air from the ambient atmosphere at desired flow rates to provide the air-fuel mixture for the low-speed and deceleration operations of the engine, an auxiliary fuel passage providing communication between said fuel supply reservoir and said main mixture circuit so as to supply additional fuel to said main mixture circuit, a suction-operated piston valve assembly for opening and closing said auxiliary fuel passage in response to the temperature of the engine, an auxiliary air passage providing communication between said suction-operated piston valve assembly and said carburetor induction passage downstream of said throttle valve for supplying additional air to said carburetor induction passage, and a bimetallic device for controlling the opening and closing operations of said suction-operated piston valve assembly in response to the temperature of the engine for thereby supplying to the engine an appropriate amount of enriched air-fuel mixture for the initial ''''cold-engine'''' and subsequent warming-up operations, said suction-operated piston valve assembly including first and second portions, said first portion consisting of a housing mounted on the outside surface of the carburetor and having a suction chamber and an air vent from the ambient atmosphere, an axially movable suction-operated piston accommodated in said suction chamber, said suction chamber communicating with said auxiliary air passage through an orifice and with said fuel supply reservoir through a bore, an axially movable piston rod accommodated in said bore and connected to said suction-operated piston, said axially movable piston rod extending into said fuel supply reservoir, and a compression spring biasing said piston rod toward said fuel supply reservoir, and said second portion consisting of a housing mounted in the body of the carburetor below the level in the liquid fuel in said fuel supply reservoir, a fuel chamber defined in said second-mentioned housing and leading to said auxiliary fuel passage through a bore and communicating with said fuel supply reservoir, an axially movable needle element accommodated in said second-mentioned housing and in abutting engagement with said axially movable piston rod at their ends and a compression spring selected to be weaker in force than the first-mentioned compression spring and biasing said needle element in a direction opposite to that of the first-mentioned compression spring, said needle element having a radially extending tapered portion for shutting off the fuel flow through said second-mentioned bore, whereby with no vacuum present in said suction chamber said piston rod forces said needle element in a direction to open said second-mentioned bore, while with a vacuum present in said suction chamber said piston rod is urged due to the vacuum in a direction to close the second-mentioned bore, and said bimetal device including a bimetal member mounted outside the first-mentioned housing of said suction-operated piston valve assembly and carrying a conical member to be seated air-tightly on said air vent, said bimetal member being adapted to hold Said conical member so as to close said air vent when the engine is cold and being adapted to bend away from said air vent so as to open said air vent as soon as the temperature of the engine exceeds a predetermined value. 